Both froggie2006 and tegu24 have hit a few critical points:
1. Marines will attempt to eat anything not their own size ... including smaller marines!
2. When stressed, Marines 'could' hurt/kill tank mates with their secreted toxins; and
3. Escaped or roughly handled marines could be a toxic threat to other household pets/ small children/ inattentive adults. I've added a variety of references beow ... the italics are my own for emphasis. I hope the prove to be of some modest value in helping you to further research the care and safety implication of keeping these impressive (and to me beautiful) animals.
respects
Wes
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Global Invasive Species Database - Bufo marinus (Compiled by: Invasive Species Specialist Group (ISSG) {Excerpts}
Taxonomic name: Bufo marinus (Linnaeus, 1758)
Synonyms: Bufo agua Clark 1916, Bufo marinis [sic] Barbour 1916, Bufo marinus marinus Mertens 1972, Bufo marinus Mertens 1969, Bufo marinus Schneider 1799, Bufo strumosus Court 1858
Common names: Aga-Kröte (German), bufo toad, bullfrog, cane toad (English), crapaud (Caribbean), giant American toad (English), giant toad (English), kwapp (Caribbean), macao (Dominican Republic), maco pempen (Dominican Republic), Maco toro (Dominican Republic), marine Toad, Suriname toad
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Secretions from the parotoid glands are produced when the toad is provoked or localised pressure is applied to it, such as a predator grasping the toad in its mouth (NRM, 2001). The toxic secretions are known to cause illness and death in domestic animals that come into contact with toads, such as dogs and cats, and wildlife, such as snakes and lizards.
Cane toads are able to squirt the toxic secretion over a metre (yard) when threatened (Lever, 2001), causing extreme pain if rubbed into the eyes (NRM, 2001). Human fatalities have been recorded from the cane toad, following ingestion of the eggs or adults (Lever, 2001) and there is a risk to children from their toxin.
Uses
Bufotenine toxin produced by B. marinus is used as an aphrodisiac and hair-restorer in Japan. In mainland China it is used to lower the heart rate of patients undergoing cardiac surgery (Musgrave, 1996). The toxin is also used by South American Indians to add to hunting arrows. The toxin has and is sometimes used as a narcotic by some people. (Lever, 2001).
http://www.issg.org/database/species/ecology.asp?si=113&fr=1&sts=
Cane Toads, Giant Toads or Marine Toads (Bufo marinus) by the Australian Museum {Excerpts}
Toxicity
All stages of the Cane Toad's life-cycle are poisonous. The venom produced by the parotoid glands acts principally on the heart. No humans have died in Australia from Cane Toad poison but overseas, people have died after eating toads and even soup made from boiled toad eggs. Cane Toads are also poisonous to pets and in Hawaii up to 50 dogs a year have died after mouthing Cane Toads. Signs of poisoning through ingestion include profuse salivation, twitching, vomiting, shallow breathing, and collapse of the hind limbs. Death may occur by cardiac arrest within 15 minutes.
Australian native fauna that have been killed by eating or mouthing Cane Toads include goannas, Freshwater Crocodile, Tiger Snake, Red-bellied Black Snake, Death Adder, Dingo and Western Quoll.
A Cane Toad responds to threat by turning side-on so its parotoid glands are directed towards the attacker. The venom usually oozes out of the glands, but toads can squirt a fine spray for a short distance if they are handled roughly. The venom is absorbed through mucous membranes such as eyes, mouth and nose, and in humans may cause intense pain, temporary blindness and inflammation.
First Aid
First aid treatment includes irrigating (washing with a lot of water) the eyes, mouth and nose if they have been exposed to toad venom. Seek medical attention if symptoms persist. When handling any frog or toad, protect the eyes, wear gloves, and thoroughly wash hands before and after touching the animal.
http://www.amonline.net.au/factsheets/canetoad.htm
STAR-BULLETIN (Honolulu, Hawaii) 18 March 05 Bufo toads pose danger to pets (Hawaiian Humane Society)
With the beginning of spring comes a sinister danger lurking in your yard that can prove deadly for your pets, especially dogs. The danger is the cane toad (Bufo marinus).
"They are ugly and don't really look threatening," said Dr. John Kaya, a veterinarian at VCA Kaneohe Animal Hospital, "but make no mistake, bufo toads can kill some dogs in a matter of minutes."
The animal that wraps his jaws around a cane toad and ingests a big dose of the poison might have only 30 minutes to be treated.
"Since VCA Animal Hospital is open until 9 p.m. and on call 24 hours, we see lots of dogs with their frantic owners. They'll phone and say, 'I don't know what happened! My dog is stumbling around and won't stop drooling and shaking his head. What should I do?' We recommend a first-aid procedure immediately and then encourage them to bring the dog here as soon as possible," Kaya explained.
Depending on the size of the dog and how much toxin is ingested, symptoms can progress to vomiting, weakness, tightly clamped jaws, irregular heartbeat, seizures and even death.
"Each animal reacts differently to toad poisoning," said Kaya, "but it should be regarded as very dangerous."
The recommended first-aid procedure includes washing out the dog's mouth with a steady stream of water, especially along the gum line. Don't point the water down the dog's throat or allow him to swallow. For large dogs, use a water hose to thoroughly rinse out the mouth while holding the dog's head low. For small dogs, holding them over a sink and using the spray nozzle works well. Again, be careful not to shoot water directly down their throat.
Gently wipe the gums and teeth with a cotton towel to remove the sticky toxic secretions, then rinse with water again. If the dog continues to salivate or shows any other symptoms, drive to the veterinary clinic. Hopefully, by the time you get there, the symptoms will have ceased. The veterinarian can provide further treatment if needed.
Cats seem to be much more discriminating and don't bite toads as often as dogs do, but if they do, take the cat to the veterinary clinic. Cats do not tolerate having their mouths washed out like a dog, so veterinary treatment is a must to save them from the toxin.
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The dangerous part of the toad is a milky white toxin excreted from parotid glands behind their eyes. Contrary to what some believe, toads do not bite and do not spit or squirt the poison. When they feel threatened, toads squeeze this poison onto the surface of their skin. Dogs and cats are poisoned when they bite or lick the toad, or when the poison gets into their eyes. The poison is also dangerous to humans, so if you must touch a toad to move it, wear gloves or stick your hand in a plastic bag first.
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There is no antidote for the toxin, but your veterinarian can counteract the clinical signs and flush the dog's system with fluids to eliminate the poison.
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http://starbulletin.com/2005/03/18/features/story7.html
Nature's Chemical Arsenal – Churchville Nature Center (Pennsylvania)
… One potentially dangerous amphibian is the marine toad, Bufo marinus. Toads have enlarged poison glands (called paratoid glands) on the head, just behind the eye ridges. These glands are greatly enlarged on the marine toad, and if pressed, may squirt out a large dose of poison. Commonly sold in pet stores, enthusiasts should exercise care when handling these large toads. There is at least one record of a person’s losing his sight when this toxin squirted into his eyes while he was handling a marine toad. …
http://www.churchvillenaturecenter.org/news/C1873870158/E2083686819/index.html
Photo of glands ‘oozing’ toxin: http://www.vnc.qld.edu.au/enviro/etselh05.htm